The present invention is directed toward the reactive coextrusion of functionalized polymers into a multi-layered film or sheet. The subject layers are chemically adhered by covalent bonds formed from reactive groups present at the interfacial surface of the layers.
Frequently, it is desirable to adhere one layer of polymer to another in order to form laminates. This can be difficult, however, due to the incompatible nature of the respective polymers. One manner of overcoming the incompatible nature of dissimilar polymers is to incorporate a glue layer or otherwise applying a surface treatment to the surfaces of the various layers. For example, polystyrene, polypropylene laminates are prepared in U.S. Pat. No. 3,779,840 by employing a sulfonated surface treatment on one olefin with an application of an epoxy resin and U.S. Pat. No. 4,361,628 discloses the use of an adhesive layer comprising polypropylene blended with a polypropylene grafted with maleic anhydride to form nylon, polypropylene extruded laminates.
While suitable laminates can be prepared by employing adhesives or other surface treatments, better methods of bonding dissimilar polymeric films are continually sought in order to avoid the use of foreign or specialty materials such as adhesives. Non-adhesive methods would eliminate the bonding layer and allow additional layers of the component polymers to be utilized.
Attempts to form laminates in the absence of adhesives have been conducted as demonstrated in U.S. Pat. Nos. 3,589,976 for a polyethylene, polystyrene, polyethylene three-layer coextrusion; 3,809,602 for coextruded saran, acrylo-butyl-styrene laminates; and 4,350,742 for an acrylic and styrene laminate film wherein the styrene contains a minor amount of an .alpha.,.beta.-unsaturated carboxylic acid. Despite the foregoing attempts, improvements in the preparation of laminates with dissimilar polymers is still sought. This is especially true for laminates containing microlayers of polyolefin films.